3365: [Usaco2004 Feb]Distance Statistics 路程统计 点分治

听说有点分治裸题来水了一发。。回去继续搞K-D tree了。。

#include<iostream>
#include<cstdio>
#include<algorithm>
#define inf 1000000007
#define N 80005
using namespace std;
int mx[N],size[N],stack[N],dis[N];
bool vis[N];
int head[N],next[N<<1],key[N<<1],list[N<<1];
int n,m,K,cnt,root,sum,ans,top;
inline int read()
{
    int a=0,f=1; char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1; c=getchar();}
    while (c>='0'&&c<='9') {a=a*10+c-'0'; c=getchar();}
    return a*f;
}
inline void insert(int x,int y,int z)
{
    next[++cnt]=head[x];
    head[x]=cnt;
    list[cnt]=y;
    key[cnt]=z;
}
void getroot(int x,int fa)
{
    size[x]=1; mx[x]=0;
    for (int i=head[x];i;i=next[i])
        if (list[i]!=fa&&!vis[list[i]])
        {
            getroot(list[i],x);
            size[x]+=size[list[i]];
            mx[x]=max(mx[x],size[list[i]]);
        }
    mx[x]=max(mx[x],sum-size[x]);
    if (mx[x]<mx[root]) root=x;
}
void getdeep(int x,int fa)
{
    stack[++top]=dis[x];
    for (int i=head[x];i;i=next[i])
        if (list[i]!=fa&&!vis[list[i]])
        {
            dis[list[i]]=dis[x]+key[i];
            getdeep(list[i],x);
        }
}
inline int calc(int x,int now)
{
    dis[x]=now; top=0;
    getdeep(x,0);
    sort(stack+1,stack+top+1);
    int ans=0,l=1,r=top;
    while (l<r)
        if (stack[l]+stack[r]<=K) ans+=r-l,l++; else r--;
    return ans;
}
void solve(int x)
{
    ans+=calc(x,0);
    vis[x]=1;
    for (int i=head[x];i;i=next[i])
        if (!vis[list[i]])
        {
            ans-=calc(list[i],key[i]);
            root=0; sum=size[list[i]];
            getroot(list[i],0);
            solve(root);
        }
}
int main()
{
    n=read(); m=read();
    for (int i=1;i<=m;i++)
    {
        int u=read(),v=read(),w=read();
        insert(u,v,w); insert(v,u,w);
    }
    K=read(); mx[0]=n;
    root=0; sum=n;
    getroot(1,0);
    solve(root);
    cout << ans << endl;
    return 0;
}